The nucleosome, composed of an octamer of highly conserved histone proteins and associated DNA, is the fundamental unit of eukaryotic chromatin. How arrays of nucleosomes are folded into higher-order structures, and how the dynamics of such compaction is regulated, are questions that remain largely unanswered. This proposal seeks to understand the role of core histone phosphorylation in regulating higher-order chromatin structure and altering "epigenetic landscapes". More specifically, histone phosphorylation will be studied in the context of mitosis, apoptosis and DNA damage. One long-range objective of this proposal is to better understand the role that core histone phosphorylation plays in mediating "cis" versus "trans" mechanisms with an emphasis on effectors ("readers") that engage phosphorylation modifications in a context-dependent fashion. A second long-range goal of this research program is to determine the enzyme systems responsible for adding (kinases or "writers") or subtracting (phosphatases or "erasers") these phosphorylation marks. We hypothesize that histone phosphorylation acts as molecular "switches", or as part of potentially redundant, modification "cassettes" to govern critical downstream chromatin associations with key effectors to determine compaction states. Understanding the physiological substrates and sites phosphorylated by these enzymes is of paramount importance. Just as studies on histone acetylation and methylation have led to a wealth of new insights into mechanisms of transcription, we anticipate that insights into histone phosphorylation will pave the way for a better understanding of chromosome condensation and DNA repair. To achieve these goals, we will employ complementary genetic, biochemical and immunocytochemical approaches in a variety of model systems. The highly conserved nature of histone proteins, as well as the phosphorylation events and the relevant enzyme systems involved, underscore the fundamental nature of the chromatin problem for all DNA-templated processes. The close association of histone kinases, such as aurora kinase, and specialized histone variants, such as H2A.X, with oncogenesis provides strong support for an emerging view that covalent modifications of histones plays a vital role in the regulation of chromatin dynamics with far-reaching implications for human biology and disease, notably cancer. PUBLIC HEALTH RELEVANCE: Although every gene exists within every cell in the human body, only a small percentage of genes are active in any given cell type. Chromatin, DNA and associated histone proteins, is the physiological form of our genome. Dr. Allis and his colleagues favor the view that distinct patterns of covalent histone modifications (chemical groups such as phosphate) form a "histone code" that is then read by effector proteins to bring about distinct downstream events. Through such enzymatic processes, histones are believed to function like a master "on/off" switch to determine whether particular genes are active or inactive. Knowing how to control which genes to turn on or off, using therapy, could reduce the risk of certain diseases. The implications of this research for human biology and human health are far-reaching.